In liquid natural gas and other combustible product tanks, many present day safety codes and regulations require the use of an internal tank valve on any inlet or outlet lines to assure control of the combustible products in the event of a leak or rupture in such lines. Such internal tank valves are normally closed valves which are only opened positively and will return to closed when such positive opening force is released. Such internal tank valves are even designed to protect against foundation shifts and earthquakes which may break a bottom withdrawal line.
Many tanks have a sheet metal diaphragm bottom which is capable of reacting to horizontal plane forces but has no capability of reacting to vertical loads exerted upwardly. The vertical loads exerted downwardly are reacted by the prepared foundation. Thus the valve should impose not upward loads on the bottom. Additionally, the valve should be secured to the tank independent of the inlet or outlet pipe.
Internal tank valves have been used which have been of relatively small size and have been a pivoting type of check valve construction.